1. Field of the Invention
The present invention relates generally to hearing prostheses, and more particularly, to simultaneous delivery of electrical and acoustical stimulation in a hearing prosthesis.
2. Related Art
Hearing prostheses such as cochlear implants have been developed to assist people who are profoundly deaf or severely hearing impaired, by enabling them to experience a hearing sensation representative of the natural hearing sensation. For most such individuals the hair cells in the cochlea, which normally transduce acoustic signals into nerve impulses to be interpreted by the brain as sound, are absent or have been partially or completely destroyed. Cochlear implants bypass the cochlear hair cells to directly deliver electrical stimulation to the auditory nerve with this electrical stimulation being representative of the sound.
Cochlear implants have traditionally included external and internal components. A speech processor worn on the recipient's body detects external sounds using a microphone and converts the detected sounds into a coded signal utilizing an appropriate speech processing strategy.
This coded signal is then sent via a transcutaneous link to a receiver/stimulator unit implanted in the mastoid bone of the recipient. The receiver/stimulator unit processes the coded signal into a series of stimulation sequences which are then applied directly to the auditory nerve via an array of electrodes positioned within the cochlea, proximal to the modiolus of the cochlea. One such cochlear implant is set out in U.S. Pat. No. 4,532,930, the contents of which are hereby incorporated by reference herein.
With improvements in technology it is possible that the external speech processor and implanted stimulator unit may be combined to produce a totally implantable cochlear implant unit that is capable of operating, at least for a period of time, without the need for any external device. In such a device, a microphone may be implanted within the body of the recipient, for example in the ear canal or within the stimulator unit, and sound would be detected and directly processed by a speech processor within the stimulator unit, with the subsequent stimulation signals delivered without the need for any transcutaneous transmission of signals. Such a device would, however, still have the capability to communicate with an external device when necessary, particularly for program upgrades and/or implant interrogation, and to modify the operating parameters of the device.
Much effort has gone into developing stimulation strategies to provide for device customization to produce the best available percepts for the prosthesis recipient. Nevertheless it is acknowledged in the cochlear implant field that the percepts produced by pulsatile electrical stimulation often sound unnatural and somewhat harsh. Many recipients adapt to this sound and, after some time, even find it natural. This is not always the case, however, and some recipients may experience difficulties. For example, for some recipients having residual hearing, the expectation of harsh and/or unnatural sounding percepts produced by a cochlear implant has been less attractive than simply persisting with residual hearing, usually assisted by an acoustic hearing aid.